document metric column prefix for mysql and mssql

docs/sources/features/datasources/mssql.md

@@ -148,7 +148,7 @@ The resulting table panel:
 
 ## Time series queries
 
-If you set `Format as` to `Time series`, for use in Graph panel for example, then the query must must have a column named `time` that returns either a sql datetime or any numeric datatype representing unix epoch in seconds. You may return a column named `metric` that is used as metric name for the value column. Any column except `time` and `metric` is treated as a value column. If you omit the `metric` column, tha name of the value column will be the metric name. You may select multiple value columns, each will have its name as metric.
+If you set `Format as` to `Time series`, for use in Graph panel for example, then the query must must have a column named `time` that returns either a sql datetime or any numeric datatype representing unix epoch in seconds. You may return a column named `metric` that is used as metric name for the value column. Any column except `time` and `metric` is treated as a value column. If you omit the `metric` column, tha name of the value column will be the metric name. You may select multiple value columns, each will have its name as metric. If you return multiple value columns and a column named `metric` then this column is used as prefix for the series name.
 
 **Example database table:**
 

docs/sources/features/datasources/mysql.md

@@ -103,7 +103,7 @@ The resulting table panel:
 
 If you set `Format as` to `Time series`, for use in Graph panel for example, then the query must return a column named `time` that returns either a sql datetime or any numeric datatype representing unix epoch.
 Any column except `time` and `metric` is treated as a value column.
-You may return a column named `metric` that is used as metric name for the value column.
+You may return a column named `metric` that is used as metric name for the value column. If you return multiple value columns and a column named `metric` then this column is used as prefix for the series name.
 
 **Example with `metric` column:**